/*
 * Copyright (c) 1997, 2003, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.lang.ref;

// Android-changed: Javadoc change to recommend against using SoftReferences for caches.
/**
 * Soft reference objects, which are cleared at the discretion of the garbage collector in response
 * to memory demand.
 *
 * <p>Suppose that the garbage collector determines at a certain point in time that an object is <a
 * href="package-summary.html#reachability">softly reachable</a>. At that time it may choose to
 * clear atomically all soft references to that object and all soft references to any other
 * softly-reachable objects from which that object is reachable through a chain of strong
 * references. At the same time or at some later time it will enqueue those newly-cleared soft
 * references that are registered with reference queues.
 *
 * <p>All soft references to softly-reachable objects are guaranteed to have been cleared before the
 * virtual machine throws an <code>OutOfMemoryError</code>. Otherwise no constraints are placed upon
 * the time at which a soft reference will be cleared or the order in which a set of such references
 * to different objects will be cleared. Virtual machine implementations are, however, encouraged to
 * bias against clearing recently-created or recently-used soft references.
 *
 * <h3>Avoid Soft References for Caching</h3>
 *
 * In practice, soft references are inefficient for caching. The runtime doesn't have enough
 * information on which references to clear and which to keep. Most fatally, it doesn't know what to
 * do when given the choice between clearing a soft reference and growing the heap.
 *
 * <p>The lack of information on the value to your application of each reference limits the
 * usefulness of soft references. References that are cleared too early cause unnecessary work;
 * those that are cleared too late waste memory.
 *
 * <p>Most applications should use an {@code android.util.LruCache} instead of soft references.
 * LruCache has an effective eviction policy and lets the user tune how much memory is allotted.
 *
 * @author Mark Reinhold
 * @since 1.2
 */
public class SoftReference<T> extends Reference<T> {

  /* J2ObjC removed.
   * Timestamp clock, updated by the garbage collector
  private static long clock;
  */

  /* J2ObjC removed.
   * Timestamp updated by each invocation of the get method.  The VM may use
   * this field when selecting soft references to be cleared, but it is not
   * required to do so.
  private long timestamp;
  */

  /**
   * Creates a new soft reference that refers to the given object. The new reference is not
   * registered with any queue.
   *
   * @param referent object the new soft reference will refer to
   */
  public SoftReference(T referent) {
    super(referent);
    // J2ObjC removed.
    // this.timestamp = clock;
  }

  /**
   * Creates a new soft reference that refers to the given object and is registered with the given
   * queue.
   *
   * @param referent object the new soft reference will refer to
   * @param q the queue with which the reference is to be registered, or <tt>null</tt> if
   *     registration is not required
   */
  public SoftReference(T referent, ReferenceQueue<? super T> q) {
    super(referent, q);
    // J2ObjC removed.
    // this.timestamp = clock;
  }

  /* J2ObjC removed.
    * Returns this reference object's referent.  If this reference object has
    * been cleared, either by the program or by the garbage collector, then
    * this method returns <code>null</code>.
    *
    * @return   The object to which this reference refers, or
    *           <code>null</code> if this reference object has been cleared
  public T get() {
      T o = super.get();
      if (o != null && this.timestamp != clock)
          this.timestamp = clock;
      return o;
  }
  */
}
